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ENSO Update

20 February 2008

Summary

La Niña conditions continue in the central and eastern equatorial Pacific. Below-average sea surface temperatures (SSTs) exist across nearly the entire equatorial Pacific, and fan out into the sub-tropical eastern Pacific. Based on the latest observations and forecasts, there is a 95% probability of maintaining La Niña conditions over the coming season.

General Discussion

The state of the tropical Pacific remained largely unchanged over the past month. La Niña conditions, which have been in place since August 2007, are indicated by substantially below-average sea surface temperatures in the central and eastern equatorial Pacific and reduced equatorial heat content. The sea surface temperature anomalies are below -2 C throughout much of the central equatorial Pacific. Low-level wind anomalies show divergence away from the region of cooler-than-average sea temperatures, leading to easterly anomalies in the Western Pacific and westerly anomalies in the Eastern Pacific. Persistence of La Niña conditions is highly likely through at least the next couple months given the current magnitude and spatial extent of the oceanic temperature anomalies.

Out of a large set of dynamical and statistical forecast models, most models indicate continuation, but gradual weakening, of the strong La Niña conditions through early 2008. Overall, based on model forecasts and current observations of the ocean surface and subsurface, the probability of a La Niña is estimated at 95% for the Feb-Mar-Apr season in progress. The probability of returning to ENSO-neutral conditions increases to the climatological value of 50% in the latter half of 2008.

Note 1 - Only models that produce a new ENSO forecast every month are included in the above statement.

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